Gerard worked as an interpreter because he could speak multiple languages: English, French, Sioux, Arikara, and Chippewa. Gerard was hired by Lieutenant Colonel Custer to serve at
Fort Abraham Lincoln as an interpreter for his
Arikara "Ree" scouts, as he was very familiar with the language from his years as a trader. He had lived in Indian country for 31 years at the time and had been involved in several battles. About dawn on the morning of June 25, 1876, Gerard accompanied Custer and the scouts to a high bluff known as the "Crow's Nest" to view the
Little Bighorn River valley below. The scouts could see dust kicked up by an immense pony herd, and claimed to see hundreds of lodges, indicating the presence of thousands of Indians. Custer was unable to see what they were describing and was unwilling to listen to their cautions. Not long afterwards, Gerard rode to a small knoll and saw 40 Indians riding off at the gallop. He shouted back to Custer, "Here are your Indians, running like devils!" Custer soon divided his company into four detachments and attacked. As Major
Marcus Reno's battalion, Gerard, and the Rees forded the river, to their surprise they saw large swarms of mounted warriors riding towards them to give battle instead of fleeing at the approach of the cavalry as Custer had presumed. Gerard turned back and overtook Custer's
adjutant, Lieutenant
William W. Cooke and Captain
Myles Keogh, another officer from Custer's column who had accompanied Reno as far as the river. Explaining that the Indians were not fleeing at all but were coming out to fight, Gerard wheeled to rejoin Reno. Cooke and Keogh rejoined Custer and were killed with him and the companies he led. When Reno retreated to the bluffs from the timber, Gerard was one of about a dozen men left behind. He and Billy Jackson joined Lt.
Charles DeRudio and Private Thomas O'Neill, and the four of them spent the rest of the 25th and most of the 26th hiding in the woods. About midday on the 26th, they were discovered by some Indians, and Gerard and Jackson, who had retained their horses, rode off to draw the Indians away from DeRudio and O'Neill, who had lost their mounts. Gerard served as Dr. Henry Porter's surgical assistant on Reno Hill. Gerard survived the battle and later testified before the Reno Court of Inquiry. In the official transcripts of the Reno Inquiry, his name is misspelled as "Girard". ==Later years==